Combined thermogravimetry/mass spectrometry and thermogravimetry/Fourier transform infrared spectroscopy combine the direct measurement of weight loss as a function of reaction temperature with the use of spectroscopic detectors for the qualitative and quantitative determination of evolved volatile products to provide kinetic information about the specific reaction mechanisms. Although offering substantial advances in the areas of detection and analysis, the presence of a component at very low concentrations may be masked by higher concentrations of interferants. Additional steps such as collecting the products in a trap or on the head of a capillary column have been employed for increasing off-gas product detection sensitivity. However, these methods necessarily introduce additional time in the detection/analysis method and result in a loss of the time/temperature evolution data for the products analyzed. Unfortunately, it is frequently most desirable to obtain a time correlation of what is occurring in the reaction of the sample with the reaction gas introduced into the reaction tube.
Another approach to obtaining a time correlation of the reaction process involves increasing the gas flow through the reaction tube while correspondingly increasing the sampling rate. This approach does not compromise the performance of the thermal system or the IR system, and avoids the prior art problems encountered with an excess pressure within the reaction tube which tends to reduce the stability of weight changes of the sample. Unfortunately, this approach renders it more difficult to detect the off-gas products by decreasing the signal-to-noise ratio at the detectors.
The present invention addresses the aforementioned limitations of the prior art by providing a sampling arrangement for a thermal gravimetric analyzer which removes the off-gas products immediately adjacent to the sample holder and provides the thus removed concentrated off-gas products directly to mass and/or IR spectroscopic detectors.